172 



NATURE 



\ytine 13, 1878 



ature ; and these zones are cup- or saucer-shaped, having 

 a general relation to the depth in different parts of the 

 Gulf, and sometimes coming to the surface at variable 

 distances from the coast. In every case, however, the 

 relative position of the zones is strictly accordant with 

 their relative specific gravities j the overlying of a warmer 

 by a colder zone being due to the dilution of the latter by 

 the admixture of fresh water, as appears from the fol- 

 lowing examples : — 



A similar alternating temperature-stratification has been 

 recently observed by the Norwegian Expedition in the 

 seas between the coast of Norway and the Faroes ; and I 

 venture to predict that when the temperatures of the suc- 

 cessive strata shall hare been correlated with their 

 respective salinities (which are modified by the admixture 

 of fresh water discharged from the Norway fiords), the 

 stratification will be found conformable to the same law 

 of the heaviest water lying deepest. 



There is one locality not far distant from our shores, 

 in which similar influences have been found to pro- 

 duce equally decided, though less strongly- marked effects ; 

 I refer to the Baltic Straits, in which very careful 

 observations of teitiperature and specific gravity have 

 now been carried on for several years under the able 

 direction of Dr. Meyer of Kiel, and his coadjutors. 

 Here there is an admixture of waters from three 

 different sources — the North Sea, the Baltic, and the 

 underflow of glacial water which is brought as far south 

 as the Skagerrack by a comparatively deep channel lying 

 outside the Norway fiords. The North Sea brings water 

 of ordinary salinity and of a temperature corresponding 

 generally to that of the air : the Baltic outflow brings 

 a variable quantity of water of low salinity : and the deep 

 Norwegian channel brings water of very low tempera- 

 ture. In addition to these factors, there is the operation 

 of winds and tides, which greatly modify the movements 

 alike of the superficial and of the deeper strata. These 

 influences are now so well understood, that, by a careful 

 correlation of them, the temperature and salinity of the 

 waters at the various observing-stations may be closely 

 predicted; very small differences in specific gravity on 

 the one hand, or small variations in level (and there- 

 fore in downward pressure) produced by winds and 

 tide?, being sufficient to determine movements in great 

 masses of water, tending to the restoration of the dis- 

 turbed equilibrium. In fact, as Dr. Meyer assured me 

 during a recent visit to this country, "Your trough- 

 experiment is being daily carried out on the great scale in 

 the Baltic Straits, with the like results." 



It is now well-established that the Temperature-stratifi- 

 cation of the Sea has, as Mr. Hind says, a7i all-i7nportant 

 bearing on the great fisheries : — " It determines the ver- 

 tical positions in the sea, of the zones of minute and 

 microscopic life which constitute the food of the higher 

 forms, up to those of the fish Avhich feed either directly 

 or indirectly upon them." The cold of the Arctic seas is 

 commonly supposed to be inimical to animal life ; but 

 hat the very contrary is the fact, is shown by the abun- 



dance of fish along those parts of the British North 

 American coast, whose waters are most reduced in tem- 

 perature by the Greenland and Labrador current, as 

 compared with their paucity along the New England 

 shores, which are less affected by that current. The 

 most noteworthy case is that of the Strait of Belle Isle, 

 in which, though almost every square mile has been an- 

 nually fished for more than two centuries, continued pro- 

 ductiveness is the rule through an average of years. And 

 thus it becomes clear that the relative extent of the cold- 

 water areas which feed (so to speak) the several fishing- 

 grounds of the North American coast, must be a factor 

 of the greatest importance in determining their respec- 

 tive values. Thus, while the water-area within the 100 

 fathoms' line along the coast of the United States north 

 of Cape Hatteras does not exceed 45,000 miles, that of 

 the British-American coasts within the same limit of 

 depth exceeds 200,000 square miles. And while the 

 former is bounded more or less closely by the heated 

 w^ater of the Gulf Stream, which invades it during the 

 summer months by a swing towards the shore, the latter 

 is only bordered by the Gulf Stream along its southern 

 edge, and is continuous to the north and north-east with 

 a limitless sea of cold water, which is the home of those 

 minute forms of marine life that constitute— directly or 

 indirectly — the source of our "commercial" fishes, the 

 cod, herring, and mackerel. 



Another advantage possessed by the fishing-grounds of 

 British North America over those of the United States, is 

 their immunity from the ravages of the blue-fish — a vora- 

 cious wandering fish, whose home is in warm southern 

 waters, its northward migration taking place only during 

 summer, and never extending far beyond Cape Cod. Its 

 destructive agency has had much to do with the dimi- 

 nished productiveness of the New England fisheries; 

 and further south is specially exerted on the mackerel 

 schools. According to the estimate of Prof. Baird, the 

 United States Fishery Commissioner, the weight of fish 

 consumed by the blue-fish of the United States coast 

 during the season is about 300,000 inillion pounds. In 

 its turn the blue-fish is largely consumed as an article of 

 human food, being taken in great numbers along the 

 coast of the Southern States ; but it is not suited for 

 salting, and is consequently of no value as an export fish. 

 From the fishing-grounds in which the blue-fish is taken 

 in immense quantities during the early winter months, 

 for the supply of the northern markets, British American 

 fishermen are excluded. 



Of the influence which Temperature has now been 

 ascertained to exert over the habits (especially the migra- 

 tions) of these fishes, and consequently over the produc- 

 tiveness of the great " harvest of the sea" furnished by 

 them, as to which a valuable mass of information has 

 been brought together by Mr. Hind, I shall give some 

 account in a future communication. 



William B. Carpenter 



THE MICROPHONE "■ 



THE following expei-iments were suggested by the 

 description, which appeared in a recent number of 

 Nature, of the microphone lately invented by Professor 

 Hughes. Instead of the pointed piece of carbon sup- 

 ported between two pieces of the same material as used 

 by him, it occurred to me that ordinary gas cinders 

 would be likely to answer the purpose tolerably well. To 

 test this, I included in the circuit of an ordinary Bell 

 telephone, a single Leclanche cell, and a small jelly can 

 half filled with cinders broken into pretty coarse frag- 

 ments. The connections were made by slipping down at 

 opposite sides, between the cinders and the sides of the 



I Abstract of a paper read before the Royal Society of Edinburgh on 

 June 3, 1878, by James Blyth, M.A., F.R.S.E. 



